Primary horn antenna feeding planar reflector through hole in focused curved reflector



Jan. 12, 1965 M. WALES 3165,747

PRIMARY HORN ANTENNA FEEDING PLANAR REFLECTOR THRO IN FOCUSED CURVED REFLECTOR Filed Feb. 15, 1965 1 UGH HOLE Hal /-0 /-'2 /-'4 1 6 /'-a 2'-o 2-2 2 4 2 6 mu: 0F r ORB/NATE EXPRESSED IN F \NVENTOR mM in! 41M .2;

ATTORNEY-5 PRIMARY HGRN ANTENNA FEEDING PLANAR REFLEQTGR THRQUGH HGLE IN FGCUSED CURVED REFLECTUR Michaei. Wales, Durham, England, assignor to The Marconi Company Limited, a British company Filed Feb. 15, 1963, Ser. No. 258,702 Claims priority, application Great Britain, Apr. 4, 71%2,

Edd U62 i i Qfiiairns. (Cl. 343-361) This inventionrelates to aerial systems and has for its object to provide improved and simplified wide aperture aerial systems which, when employed for transmission, will provide at the aperture a substantially parallel beam of radio energy from a localised primary source. As will be apparent later, the invention provides aerial systems which will give much the same performance as the well known Cornucopia type of radiohorn but which are structurally much simpler and cheaper.

The invention will be described hereinafter with reference to transmission but, as will be obvious later, systems in accordance with this invention can equally well be used for reception. Expressions such as, localised pri- United States Patent Office Patented Jan. 12, 1%55 away from the mouth of the whole aerial system. The angle between the curved reflector and the planar reflector need not be fixed and constant but the said planar reflector may be hinged at one edge and moveable back and forth over an are so that said angle isvariable. Such an aerial system is useful, for example, in a height-finding radar.

The invention isillustrated in and further explained in connection with thedrawings, inwhich: FIGURE 1 is a schematic side view of one embodiment; FIGURE 2 waveguide mouth-"2 (not shown in FIGURE 2), Opposite and facing the mouth 2 is a planar reflector 3.

mary radio unitare therefore intended to include localised primary radiation sources such, for example, as a waveguide mouth which is fed from a transmitter and which may, from the practical point of view, be regarded as approximating to apoint source, and localisedreceiver feeds such, forexample, as a similar Waveguide mouth feeding through a waveguide into a receiver.

According to this invention, an aerial system comprises a curved reflector, a localised primary radio unit in a hole in said reflector and a planar reflector opposite and facing said primaryunit andin a plane at an angleto the curved reflector, the positioning of said planar reflector and the shapes and mutual arriangement of the two -rei flectors being such that radio energy followingvstraight line paths from said primary unit to the planar reflector twill'be reflected thereby to the curved reflector and reflected again from the curved reflector along paths parallel to one another and to the plane of the planar According to a feature of this invention, an aerial system comprises a reflector of paraboloidal curvature, a

localised radio unit in a hole in the paraboloidal reflector, a planarreflector opposite and facing saidprimary Radial sidewalls 4 connect the curved edges of the reflector 1. with the adjacent edges of the reflector 3. The cross indicated at 5 in FIGURE 1 represents the focus of the paraboloid. If the mouth of the horn 2 is in the curved surface of the reflector 1, the distance 2F (see FIGURE 1 should be twice the distance F. If, as illustrated, the horn mouth projects a little way in the direction of the reflector 3, the distance shown'as F should be correspondingly reduced. The chain lines in FIGURE 1 representenergy paths from thehornvia the reflectors, 3 and 1 to form the final emergent parallel beam and are drawn on the assumption, which is near enough for prac H tical purposes, that the mouth 2 isa point source in then surface of the reflector ll.

. The arrangement of FIGURES I and2," simple strucf turallythough it is, gives good performance and gain with high aperture efliciency and low noise characteristics approximating to those of the considerablymore expen I sive Cornucopia horn, though ,the bandwidth may be rather less. As will be appreciated the invention operates by the production of a virtual source (at the 'focus) unit and in a plane at an angle to the paraboloidal reflector, the distance of said planar reflector from said radio .unit being at least approximately one 'half the distance ofthe focus of theparaboloid from .saidunit, and a the two curved edges of the paraboloidal reflector and an adjacent edge of said planar reflector, the whole arrangement being such that radio energy following straight line paths from said unit to the planar reflector will be reflected thereby to the curved reflector and reflected again from the curved reflectoralong paths par- "pair of flat side walls which extend each between one of allel to one another and to the plane ofthe. planar refiector. V

Preferably the localised primary radio unit'is, a small 'radio horn orflared waveguide mouth. Its mouth can lie in the general surface of the curved reflector but, if-

desired, it can be allowed to project a little beyond said surface in the direction ofthe planar reflector which, in this case, should be shifted in correspondence with the shift of the horn or waveguide mouth with respect to the position it would occupy'were'it in said curved surface.

Preferably also the axis of the localised primary radio unit is tilted'a few degrees, e.g., about 6, away from thesnorrnal to the flat reflector in the direction of the rear part of the curved reflector, i.e., in the direction tenuation is approximately constant. In FIGURE 3 the i V ing f from a real source (the mouth 2);, Electrically both the real and ,virtual sources Lare well within the". aperture p 1 plane of the paraboloidal sector and there is good screeni v om extraneous radiation (primarily back radiation) and high gainand efficiency. f i

In practice, the realsourc e 2 will normally be a small horn of the order of two wavelengths aperture sizeand the diffraction field will be'dorninant. This, however, does not seriously alter conclusions drawn from considering the operation in terms of geometricab optics with a,

point source (real source), as is done in drawing the chainline paths of FIGURE 1, provided, of course, that a unique phase centre is preserved and the secondary aperture amplitude pattern is modifled in accordance. with the amplitude pattern obtained from the primary horn.

of the paraboloid sector. This tilt is desirable for two reasons (a) the illumination in the vertical plane is optimised. for maximum aperture efficiency and (12) the reflections returned from the flat {reflector 3 to the primary horn aperture'are reduced. The illumination in curvature is small and, as a consequence, the space at- FIGUREB shows the aperture illuminationin the yer-i tical plane (ordinates-mints offield intensity) of. the aperture fo r'the case where a. beam tilt of-6" is made'by the primary horn 2 towards thewrear part-0f the surface the horizontal plane is approximately the primary horn illumination in this plane, as the degree of reflector abscissae are values of the Y (vertical) ordinate expressed in terms of F (focal length). The flat reflector 3 intercepted about 85% of the primary horn energy in the case for which FIGURE 3. was obtained.

shown in full lines in its central position and in dotted lines in its-two'extreme positions. The-result of swing-- ing the planar reflector is, of course, to swing the emer-; gent beam up and down over an arc in the plane of the paper in FIGURE 4. Side plates (not shown in FIG- URE 4) may be provided as at 4 in FIGURE 2 but, it pro- ,vided they cannot of course be fixed to the side edges of the reflector 3 which swings between them with as small a clearance therefrom as is convenient to permit of swinging.

I claim:

1. An aerial system comprising a curved reflector having a predetermined focus, a localised primary radio unit in a hole in said reflector, and a planar reflector opposite and facing said primary unit and in a plane at an angle tothe curved reflector, the distance of said planar reflector from said primary unit being at least approximately one-half the distance of said focus from said unit, and theshapes and mutual arrangement of the two reflectors being such that radio energy following straight line paths from said unit to the planar reflector will be reflected'thereby to the curved reflector and reflected 'again from the curved reflector along paths parallel to one another; and to'the plane of the planar reflector.

1 2. Anaerial system comprising a reflector of paraboloidal curvature, a localised radio unit in a hole in the paraboloidal reflector, a planar reflector opposite and facingsaid primary unit and in a plane at an angle to the paraboloidal reflector, the distance of said planar reflector from said'unit being at least approximately one-half the distance of the focus ,of the paraboloid from said unit, and a pair of flat side ,walls which extend each between one of, the two curved edges of the paraboloidal 1 reflector and an adjacent edge of said planar reflector,

the whole arrangement being such that radio energy following straight line paths from said unit to the planar reflector will be reflected thereby to the curved reflector 5 and reflected again from the curved reflector along paths.

parallel to one another and to the plane of the planar reflector.

a 3. An aerial system as claimed in claim 1 wherein the radio unit is a small radio horn.

4. An aerial system-as claimed in claim 1 wherein the radio unit has a mouth lying in the general surface of the curved reflector.

(a? 5. An aerial systemas claimed in clairn 1 wherein the radio unit has a mouthprojecting a small distance be- 5 yond the general'surface of the curved reflector in the direction of the planar reflector, the position of the planar reflector being shifted in correspondence with the shift.

of the horn or waveguide mouth with respect to the position it would occupy were it in said curved surface.

' 6. An aerial system as claimed in claim 1 wherein the axis of the localised primary radio unit istilted a few degrees away from the normal to the planar reflector in the direction of the rear part of the curved reflector.

7. An aerial system as claimed in claim 1 wherein the planar reflector is fixed.

. 8. An aerial system as claimed in claim 1 wherein the planar reflector is hinged so as to be movable back and a forth over an are so that its angle'to the curved reflector is variable.

"9. An aerial system as claimed in claim 1 wherein the radio unit is a flared waveguide mouth.

HERMAN KARL SAALBACH, 215mm Examiner. 

1. AN AERIAL SYSTEM COMPRISING A CURVED REFLECTOR HAVING A PREDETERMINED FOCUS, A LOCALISED PRIMARY RADIO UNIT IN A HOLE IN SAID REFLECTOR, AND A PLANAR REFLECTOR OPPOSITE AND FACING SAID PRIMARY UNIT AND IN A PLANE AT AN ANGLE TO THE CURVED REFLECTOR, THE DISTANCE OF SAID PLANAR REFLECTOR FROM SAID PRIMARY UNIT BEING AT LEAST APPROXIMATELY ONE-HALF THE DISTANCE OF SAID FOCUS FROM SAID UNIT, AND THE SHAPES AND MUTUAL ARRANGEMENT OF THE TWO REFLECTORS BEING SUCH THAT RADIO ENERGY FOLLOWING STRAIGHT LINE PATHS FROM SAID UNIT TO THE PLANAR REFLECTOR WILL BE REFLECTED THEREBY TO THE CURVED REFLECTOR AND REFLECTED AGAIN FROM THE CURVED REFLECTOR ALONG PATHS PARALLEL TO ONE ANOTHER AND TO THE PLANE OF THE PLANAR REFLECTOR. 